Relatively recent discoveries in the field of RNA metabolism have revealed that the uptake of certain double stranded RNA (dsRNA) can induce a phenomenon known as RNA interference (RNAi). RNAi is a process by which a polynucleotide directly or indirectly inhibits the expression of a gene, e.g., through inhibiting translation of messenger RNA. This phenomenon has been observed in cells of a diverse group of organisms, including C. elegans, Drosophila, and humans, providing a powerful therapeutic approach to the genetic control of human disease.
It has been shown that when short RNA duplexes are introduced into mammalian cells in culture, sequence-specific inhibition of target mRNA can be accomplished without inducing an interferon response. These short dsRNAs, referred to as small interfering RNAs (siRNAs), can, for example, act catalytically at sub-molar concentrations to cleave greater than 95% of the target mRNA in a cell. A description of the mechanisms for siRNA activity, as well as some of its applications are described in Provost et al., Ribonuclease Activity and RNA Binding of Recombinant Human Dicer, E.M.B.O.J., 2002 November, 1, 21(21): 5864-5874; Tabara et al., The dsRNA Binding Protein RDE-4 Interacts with RDE-1, DCR-1 and a DexH-box Helicase to Direct RNAi in C. elegans, Cell, 2002, June 28, 109(7):861-71; Ketting et al., Dicer Functions in RNA Interference and in Synthesis of Small RNA Involved in Developmental Timing in C. elegans; and Martinez et al., Single-Stranded Antisense siRNAs Guide Target RNA Cleavage in RNAi, Cell 2002, September 6, 110(5):563.
RNA-induced gene silencing in mammalian cells is presently believed to implicate at least one of three different levels of control: (i) transcription inactivation (siRNA-guided DNA and histone modification, for example, methylation); (ii) siRNA-induced mRNA degradation; and (iii) mRNA-induced transcriptional attenuation. Consequently, the ability to assess gene function via siRNA mediated methods, as well as to develop therapies based on siRNA-induced gene silencing, presents an exciting and valuable tool that will accelerate genome-wide investigations across a broad range of biomedical and biological research. However, application of the technology has been limited to gene silencing and has not been applied to gene activation.
There is accordingly still a need for compounds that can activate gene expression, and methods of using such compounds for the study and treatment of genetic disorders. The present invention addresses these needs, as well as others.